THE CHILDHOOD OF THE EARTH 



older date have been so eaten into and worn by the action 

 of the elements that not only the successive sheets of lava 

 are exposed but the rock floor over which they poured. 

 Exposed also are the abundant dykes which served as the 

 channels by which the lava rose to the surface. In 

 Western Europe important examples of this structure 

 occur from the north of Iceland through the inner 

 Hebrides and the Faroe Islands to Iceland. This volcanic 

 belt presents a succession of lava sheets, which even yet, 

 in spite of enormous waste, are in some places more than 

 3000 feet thick. These sheets are nearly flat and rise in 

 terraces over one another into green grassy hills or into 

 the dark fronts of lofty sea-washed precipice. Where 

 sheets have been stripped off or worn down by wind and 

 weather thousands of volcanic dykes are exposed. These 

 dykes are, as it were, the roots of which the lava sheets 

 were the branches; and even where the whole of the 

 material that gushed up to the surface has been worn 

 away the dykes remain as evidence of the vigour and 

 energy of the volcanic forces. 



o7 



